<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        const arr = [1,2,3,4,5,6,7,8,9,10]
        function splitSearch(arr, num) {
            let left = 0 
            let right = arr.length 
            
            while(left < right) {
                let midIndex = Math.floor((left + right ) / 2)
                let midValue = arr[midIndex]
                if (num < midValue) {
                    right = midIndex
                } else if (num > midValue) {
                    left = midIndex + 1
                } else {
                    return midIndex
                }
            }
            return -1
        }

        const res = splitSearch(arr, 10)
        console.log(res)
    </script>
</body>
</html>